Due to its characteristics of being easily applicable to various products and electrical properties such as a high energy density, a secondary battery is not only commonly applied to a portable device, but universally applied to an electric vehicle (EV) or a hybrid electric vehicle (HEV) that runs on an electric driving source. This secondary battery is gaining attention for its primary advantage of remarkably reducing the use of fossil fuels and not generating by-products from the use of energy, making it a new eco-friendly and energy efficient source of energy.
Secondary batteries can be classified into various types of batteries including can-type batteries with internal elements in a metallic hard case, according to the shape or structure for applications, and with the recent trend toward miniaturization of mobile devices, the demand for thin prismatic and pouch-type batteries is growing. Particularly, high attention is paid to a pouch-type secondary battery which is easy to adapt the shape, has a low production cost, and is lightweight. In addition, development and commercialization of a pouch-type secondary battery as a power source of electric vehicle or hybrid electric vehicle requiring high output and large capacity is in progress.
FIG. 1 is a plane projection view of a conventional pouch-type secondary battery, and FIG. 2 is a cross-sectional view of the pouch-type secondary battery.
Referring to FIGS. 1 and 2, the pouch-type secondary battery 10 includes a pouch case 20, an electrode assembly 30, an electrode tab 40, an electrode lead 50 and a lead film 60.
The pouch-type secondary battery 10 has a structure in which the electrode assembly 30 is received in the pouch case 20. The electrode assembly 30 received in the pouch case 20 refers to an alternating stack of a positive electrode plate and a negative electrode plate. In this instance, a separator is interposed between the positive electrode plate and the negative electrode plate to separate them. The electrode tab 40 extends from or is connected to the electrode plate for each polarity. The electrode lead 50 is connected to the electrode tab 40. The lead film 60 is for sealability and insulation of the electrode lead 50 and the pouch case 20, and is interposed between the electrode lead 50 and the inner surface of the pouch case 20. Reference symbol S indicates a sealing part by heat fusion.
The conventional pouch-type secondary battery 10 with this structure has a welded part A in the length-wise direction (or surface-wise direction) of the electrode lead 50 by joining a lower surface or an upper surface of the electrode tab 40 to an upper surface or a lower surface of the electrode lead 50 using ultrasonic welding. For this reason, the conventional pouch-type secondary battery 10 needs to have an ample space within the pouch case 20 for surface-wise direction coupling between the electrode tab 40 and the electrode lead 50.
For example, in the conventional pouch-type secondary battery 10, the welded part A is about 4 mm in width, and a non-electrode region (terrace) between the electrode assembly 30 and the pouch case 20 is about 18 mm in consideration of the width of the surface-wise direction welded part A and the sealing part S. Thus, the conventional pouch-type secondary battery 10 has a problem with the internal space utility of the secondary battery due to the presence of the surface-wise direction welded part space.